With the rapid expansion of markets for notebook computers, cellular phones, electric cars, and the like, secondary batteries with high energy density are required. Generally, a method using a negative electrode active material with large charge and discharge capacity is known as means for increasing the energy density of a secondary battery. Patent Literature 1 describes an example of a nonaqueous electrolyte secondary battery using lithium metasilicate (Li2SiO3) that is silicon oxide containing lithium or silicon dioxide (SiO2), as a negative electrode active material with large charge and discharge capacity, and using an electrolyte solution containing ethylene carbonate, as a solution of a nonaqueous electrolyte. Here, Patent Literature 1 discloses, as means for obtaining a secondary battery with high energy density, the step of electrochemically reacting silicon oxide, such as lithium metasilicate or silicon dioxide, with lithium or a substance containing lithium to obtain a negative electrode active material comprising silicon oxide containing lithium.
On the other hand, Patent Literature 2 relates to an electrode for a secondary battery in which a silicon thin film as an active material is formed on a surface of a current collector, and this silicon thin film has a configuration comprising a plurality of columnar structures. The purpose of the above configuration in Patent Literature 2 is the prevention of the occurrence of wrinkles in an electrode caused by a current collector with a silicon thin film due to repeated charge and discharge, because of a large change in the volume of the silicon thin film in the rapid charge and discharge of a secondary battery. In Patent Literature 2, by forming the shape of the above silicon thin film in such a manner that a plurality of columnar structures are arrayed, the change in the volume of the silicon thin film caused by charge and discharge is absorbed by the voids among these plurality of columnar structures, thereby preventing the deformation of the silicon thin film.
In the electrode for a secondary battery, comprising this silicon thin film, a pattern is formed on a surface of a copper foil or the like that is a current collector by a method, such as printing an ink, and after a silicon thin film is formed on the surface by sputtering or the like, the above pattern is removed by a method, such as immersing in an alkali solution. By this method, the silicon thin film according to the shape of the above pattern is formed on the current collector. By making the shape of this pattern a circular perforated pattern or the like, it is possible to form a silicon thin film comprising a plurality of columnar structures on a surface of a current collector.